1. Field of the Invention
The present invention relates generally to a magnetic recording and reproducing apparatus, such as a video tape recorder (VTR), which records a video signal in tracks recorded obliquely on a magnetic tape by means of at least one rotary head. More particularly, this invention relates to a helical-scan-type magnetic recording and reproducing apparatus which can record audio signals on video tracks. Still more particularly, this invention relates to a recording and reproducing technique which provides an echo effect to impart a feeling of presence to a listener.
2. Description of the Prior Art
Conventional helical-scan recording and reproducing apparatus have recording tracks which slant across the magnetic tape and record video signals on the tracks through the use of a rotary head. Since the audio signals are recorded by a stationary head, audio tracks lie along the elongated axis of the magnetic tape. In such magnetic recording and reproducing apparatus (VTR), the rate of feed of the magnetic tape may be reduced to expand the recording time. But when the tape feed rate is reduced, the quality of the audio signals is also reduced. To improve the quality of sound, a magnetic recording and reproducing apparatus has been developed which records the audio signals in the above-described video tracks by means of one or more rotary heads.
FIGS. 1(A) and 1(B) show an arrangement of a rotary drum and magnetic tape in the magnetic recording and reproducing apparatus mentioned above (hereinafter referred simply to as a "VTR") and its recording format on the tracks, respectively. In FIG. 1(A), the VTR includes a rotary drum 1, two rotary heads 2a and 2b, and a magnetic tape 3 wound around a portion of the periphery of the rotary drum 1 by means of guide pins 4 so that the tape 3 contacts the drum 1 over an angle of 180.degree.+.alpha., where .alpha..apprxeq.30.degree.. That rotary contact area is sometimes referred to as the "wrap angle".
The audio signal to be recorded is alternatingly provided from associated recording circuitry to the rotary heads 2a, 2b. As the magnetic tape 3 passes about the rotary drum 1, recording tracks are formed, each of which is longer than the conventional corresponding video tracks A and B by a length a and b corresponding to the angle .alpha., as shown in FIG. 1(B). Therefore, the audio signals are recorded in the form of compressed-time-axis pulse-code-modulated (PCM) audio signals on the portions a, b of the tape, sometimes called an auxiliary track. Video signals are recorded in the tracks A and B.
This recording and reproducing method is incorporated in 8 mm video tape recorders. A standard recording method for 8 mm video tape recorders is for the audio signals to be recorded on the main video tracks in the form of a so-called audio-frequency-modulated (AFM) audio signal consisting of a 1.5 MHz carrier wave which is frequency modulated by the audio signal and superposed on the video signal, and its chrominance and luminance signals, as shown in FIG. 2(A). Conventionally, the central frequency for the chrominance signal is 3.58 MHz which is converted to about 688 KHz to occupy the lowest band of the frequency spectrum on the tracks A, B of tape 3. The AFM audio signal occupies the next frequency band, centered at about 1.5 MHz, while the video luminance signal Y occupies the highest frequency band on the tracks A, B. The PCM audio signals are recorded on the auxiliary tracks a, b in a frequency range at about that of the luminance signal Y, as shown in FIG. 2(B).
Hence, in the case of 8 mm video tape recorders, both PCM audio signals recorded on auxiliary tracks a and b and the above-described AFM audio signals on the video tracks A, B can be recorded and reproduced If a stationary head is used, another audio signal component can be added.
However, since the AFM audio signals and the PCM audio signals differ in recording positions on the tape and are demodulated by different methods, these audio signals can only be used as separate musical sources. Such a technique therefore lacks flexibility in application. Usually, an AFM signal is monaural, while a PCM signal is a stereo signal Thus, it would be desirable and pleasing to the listener if the AFM signal thus recorded could simulate a stereo signal to provide a listener with a feeling of presence at the musical source. Such an effect surrounds the listener with sound.
Thus, it is an aim of this invention for such recording and reproducing apparatus to use the PCM signal and the AFM signal from a tape of the type described to provide a "surround effect" by producing an echo during reproduction of the PCM and AFM audio signals.